1. Field of the Invention
The present invention relates to a charge pump circuit, and more specifically, to a charge pump circuit which can freely control the speed of a charge pump.
2. Discussion of Related Art
A high voltage pulse that is higher than an external power supply Vcc has been widely used in DRAM circuits since it can compensate for the loss of threshold voltage of transistors. More particularly, circuits which employ the high voltage pulse include a word line driver circuit, a bit line separation circuit, a data output buffer and the like
This high voltage pulse is generated by means of a VPP circuit. Load of the Vpp circuit is usually composed of a capacitor component. Two kinds of current flow in the load of the Vpp circuit. One of the current is a minute inverse bias leakage current that always flows through a PN junction, and the other of the current is a high excessive current for driving internal circuits whenever a chip is activated. Accordingly, the VPP level can be constantly maintained only when such charge loss is compensated for.
In the prior art, if such variation in the level occurs, charge pump circuits are driven by detecting lowering in the level and charges are pumped into the capacitor, so that a lower VPP level returns to its original value. In this case, however, there is a disadvantage in that it is not easy to control the pumping speed even when more rapid return of the level is needed. In order to make the pumping speed fast, the cycle of a ring oscillator within a charge pump circuit has to be made fast. For this, after a FIB (Focused Ion Beam) work is performed on options, a test has to be performed. A mask re-work is needed according to the test result. Thus, there is problem in that lots of time and cost is consumed.